How Cytoskeletal Disorders Contribute to Errors in the Chromosomal Segregation of Oocytes and Cleavage Stage Embryos

Observations of the processes of oogenesis, fertilization, and the earliest embryonic development have given us the opportunity to estimate the importance of chromosomal distribution errors for the success of mammalian reproduction. It is now known that in the large volume of oocytes, zygotes and the first embryonic cells, the rearrangement of chromatin is associated with a complex rearrangement of cytoskeletal structures, which creates specific problems. This review discusses two main issues critical to the success of early embryos: Why oocyte meiosis is too frequently wrong in chromosomal segregation? Why the first zygotic mitoses are too frequently wrong in chromosomal segregation? We concluded the following: (1) The main cytoskeletal defects that disturb oocyte meiosis are a problematic connection between cytoskeleton and nucleoskeleton, unsuccessful movement of the spindle to the oocyte periphery, unstable anchoring of the spindle to oolemma, and deviations in meiotic spindle morphology; (2) The main cytoskeletal defects that disturb pronuclear unification are nonfunctional male centriole, unsuccessful forming of microtubule aster around the sperm centrosome, problematic movement of the two pronuclei towards each other and inappropriate contacts between centrosomes, microtubules and nuclear pore complexes; (3) Cytoskeletal defects that disturb zygote mitosis are unsuccessful forming of bipolar mitotic spindle, non-synchronized congression of maternal and paternal chromosomes, and unsuccessful attachment of kinetochores to microtubules.